In simple systems, an absolute position detector (APD) is generally used to determine the position of a moving component along a path of travel. The APD typically accomplishes this via detection of the current position of a marker affixed to or associated with the component. In more sophisticated systems, the APD is further used to determine the positional state of an assembly of interrelated moving components, such as gears, via resolution of the combined current position of a series of markers on the interrelated moving components.
APDs are commonly used in connection with an assembly of multiple rotating gears, such as may be found, for example, in valve actuator mechanisms. In a valve actuator, an APD generally detects the positional state of a series of interrelated circular gears, the positional state representative of the degree of openness of the valve. In such cases the APD monitors the paths of circular travel of markers on the interrelated gears.
Such circular travel is by no means the only type of motion monitored by APDs, however. APDs may be used to monitor position, for example, on other shaped closed loop paths, such as elliptical or irregular closed loop paths. Alternatively, APDs may be used to measure position on straight or curved paths that are not on a closed loop. Travel along such open paths may or may not be reciprocating. For example, APDs can be used to measure the state of a torque sensor in a valve actuator via monitoring of the current position of a member traveling along a pendulum-like path.
It is also well understood that absolute position detection is a dynamic operation. Successive samples of a current positional state may be resolved into a stream that forms a dynamic control tool.
The advent of computerized control has increased the need for APDs that generate high speed streams of samples that indicate current positional states in digital format. The speed and capacity of modern computers allow positional samples to be processed at a high speed. There is a particular need for APDs that generate samples at that speed. The faster the stream of samples that is processed, the finer the resolution of monitoring and control of the positional state.
For this reason, APDs relying on mechanical systems, such as cams to activate a switch or a potentiometer, are fast becoming obsolete. These devices have always suffered from backlash because of the mechanical load on the components. Wear and tear on the mechanical parts has always tended to shorten operational life. On top of these inherent drawbacks, such mechanical APDs tend not to be robust enough to be able to be operated at high speeds.
The prior art has addressed the problems of mechanical APDs by teaching use of non-contact APDs, such as those described in U.S. Pat. No. 5,640,007. This patent describes an optical encoder in which a plurality of encoder wheels each contain a series of openings that pass by a light emitting device as the gears are turned. As light is shined through these openings and detected, the openings through which light is transmitted encodes the position of the wheels, and this code is compared to a defined code sequence to determine the position of a rotatable shaft functionally connected to the position detector.
Certain types of detectors have also utilized magnetic fields to encode the position of a device and to determine the position of a rotatable shaft. A magnetic sensor apparatus is described in U.S. Pat. No. 4,728,950. The device described in the ""950 patent addresses the problem of automation of reading decimal gears, such as the type normally used in utility meters, in which each higher order digit is displaced in a 10 to 1 ratio relative to the lower digit. The devices described teach use of Hall Effect sensor devices to detect the magnetic field of a magnet attached to each digit gear. In the devices described, each gear has a permanent magnet attached thereto, and an array of 10 Hall Effect sensor devices are placed in a circular array with respect to each gear, so that the magnets pass over the sensor devices in succession as the gears turn. The resulting coded output of the sensor devices is read in a linear fashion, such that the reading of the position of the higher gears are dependent on the readings of the lower gears.
Both of the ""007 and ""950 inventions rely exclusively on normal state recognition, and indeed go to great lengths to avoid abnormal states. This reliance on normal state recognition is typical of prior art APDs. The term xe2x80x9cnormal statexe2x80x9d refers to an environment in which preselected individual sensors, and often single individual sensors, are associated with a corresponding number of discrete absolute positions available to a source. Whenever the source occupies one of those positions and activates solely the designated sensor or group of sensors for that position, the APD is in a xe2x80x9cnormal state.xe2x80x9d In contrast, whenever the source is between those positions in its path of travel, or otherwise activates more than one designated sensor or group of sensors at the same time, the APD is in an xe2x80x9cabnormal state.xe2x80x9d Returning to the ""007 and ""950 patents, these inventions are characteristic of the traditional prior art approach using exclusively normal state position detection. A key feature of these prior art inventions is to ensure that stray or unfocused emissions from the source are not recorded in error by the wrong sensor, i.e. a sensor other than the one designed to be indicative of the current absolute position. In the case of the ""007 patent, reflective surfaces are used to focus light through the apertures and onto the light sensing devices. In the case of the ""950 patent, a three-pole magnet is used to focus the magnetic field onto single Hall Effect devices in predefined normal states.
Sole reliance on normal state detection imputes a number of drawbacks and inherent limitations on APDs. First, the resolution of the APD is limited to the number of discrete sensors deployed. The APD can measure no finer a resolution than the predefined number of normal states monitored for. Further, structural or space limitations may dictate that less than an optimal number of sensors can be deployed on a particular moving component.
Second, while stray and erroneous sensory readings can perhaps be minimized, they can never truly be eradicated. This is especially true for a safe, low-cost sensory medium such as magnetic flux, which exists in more of a field than a directed beam. This is further especially true in high speed environments where the transitions between successive normal states become harder to identify. Thus, APDs relying solely on normal state detection necessarily include a lot of structure minimizing the effect of the inevitable. This structure adds to the cost and complexity of the APD, while possibly detracting from overall robustness.
This prior art tendency towards xe2x80x9cextra structure to minimize the inevitablexe2x80x9d is highlighted in U.S. Pat. No. 4,737,710. A complex combination of Hall Effect device placements, stray flux shielding, and signal adaptation circuitry is disclosed to purify detection of normal states in high speed service. It is nonetheless a fact that APDs such as illustrated in the ""710 patent exist in an abnormal state most of the time. Except when a source is momentarily directly in communication with a single sensor, the APD is effectively between sensors, and thus by definition in an abnormal state. Sole reliance on normal state detection may therefore not always be the most optimal approach.
It will therefore be appreciated that an APD that interprets detection of abnormal states, rather than avoiding them, would be highly advantageous. The disadvantages of sole reliance on normal state detection as described above would be obviated. Further, such an APD would further have good application to high speed service.
Moreover, reliance on detection of both normal and abnormal states presents opportunities for additional novelty in the process of decoding the physical state of an array of sensors into a signal suitable for digital processing. Although decoding techniques known in the art could be used, it would be further advantageous to have a decoding technique available that specifically enhances the performance and error-detection security of an APD interpreting both normal and abnormal states.
These and other objects and advantages are provided by an absolute position detector that interprets, rather than avoids, abnormal sensory states. The inventive APD allows a source to activate different combinations of sensors in an array as a marker travels along a path. The marker may be the source itself, or alternatively a moving window interposed between the sensors and a substantially stationary source. The current activation/deactivation state of the array is converted into a digital signal that is reliably indicative of the current absolute position of the marker along the path.
In a first embodiment, arrays of Hall Effect devices monitor a dynamic magnetic field whose current condition represents the current absolute position of a series of magnets traveling on a set of interrelated circular gears. In operation of the first embodiment, the current relative position of the magnets on the gears generates a specific momentary magnetic field, which in turn activates a specific group of Hall Effect devices in the combined arrays. The activated group may comprise one specific or more Hall Effect devices in each of the combined arrays, depending on the condition of the magnetic field. The current activation/deactivation state of the array is sampled, and then converted, advantageously via truth table logic, into a digital signal representative of the current positional state of the gears.
In a second embodiment, arrays of hall Effect devices monitor the pendulum-like motion of a member in reciprocating travel along an open path. The position of the member on the path indicates a detected level of torque. Again, magnets are disposed on the member so as to create different activation/deactivation states in the arrays according to different positions of the member. Truth table logic then converts the current activation/deactivation state of the array into a digital signal representative of the detected level of torque associated with the current position of the member.
As noted, both of the APD embodiments described herein practice the APD invention by detecting and encoding absolute positions via sampling the condition of sensor arrays that may be in normal and abnormal states. The conversion of these encoded absolute positions to a digital signal is actually achieved by decoding the condition of each of the sensors in the sensor array and applying truth table logic. It will be understood that this decoding function may be achieved by any preselected decoding technique that identifies the current state of the sensor array and then converts it to a computer processable code, such as binary code, Gray code, V-scan code, or alternatively a customized or proprietary code.
The APD invention according to one aspect is therefore embodied in a device for detecting the positional state of an incrementing multi-gear assembly, comprising:
an assembly of components in geared relationship, each component disposed to rotate, said geared relationship enabling the rotation of one component to increment a next component in sequence;
a plurality of said components each including a system further comprising:
a source affixed to the component and traveling along a predefined circular path as said component rotates; and
an array of at least three sensors deployed equidistantly around the path of the source, different combinations of sensors within the array disposed to become activated and deactivated via sensory communication with the source as the source travels its path, said different combinations ranging from one sensor to multiple sensors activated by the source at different times during travel along the path by the source; and
a converter, the converter disposed to convert current combined activation/deactivation states of sensors in each system into a digital signal representative of a current overall positional state for the assembly.
According to a second aspect, the APD invention is further embodied in a method for establishing the position of a marker disposed to travel along a predefined path, the method comprising: (a) deploying an array of at least two sensors along at least a part of the path of the marker, different combinations of sensors within the array disposed to become activated and de-activated via sensory communication with at least one source as the marker travels its path, said different combinations ranging from one sensor to multiple sensors activated by at least one source at different times during travel along the path by the marker; and (b) converting current combined activation/deactivation states of the sensors in the array into a digital signal representative of a current position for the marker along the path.
According to a third aspect, the APD invention is further embodied in a device for detecting the positional state of a geared assembly, comprising:
a plurality of moving components in geared relationship;
a plurality of said moving components each including a system further comprising:
a marker affixed to the moving component and traveling along a predefined path as said component moves; and
an array of at least two sensors deployed along at least a part of the path of the marker, different combinations of sensors within the array disposed to become activated and deactivated via sensory communication with at least one source as the marker travels its path, said different combinations ranging from one sensor to multiple sensors activated by at least one source at different times during travel along the path by the marker; and
a converter, the converter disposed to convert current combined activation/deactivation states of sensors in each system into a digital signal representative of a current overall positional state.
According to a fourth aspect, the APD invention is further embodied in a positional detector, comprising: a moving component; a marker affixed to the moving component and traveling along a predefined path as said component moves; an array of at least two sensors deployed along at least a part of the path of the marker, different combinations of sensors within the array disposed to become activated and deactivated via sensory communication with at least one source as the marker travels its path, said different combinations ranging from one sensor to multiple sensors activated by at least one source at different times during travel along the path by the marker; and a converter, the converter disposed to convert current combined activation/deactivation states of sensors in the array into a digital signal representative of a current position for the marker along its path.
According to a fifth aspect, the APD invention is embodied in a device for detecting the position of a rotating member traveling in pendulum motion, the device comprising: a source affixed to the member, the source moving in reciprocating motion along a path described by a circular arc, an array of at least three sensors deployed equidistantly around the path of the source, different combinations of sensors within the array disposed to become activated and deactivated via sensory communication with at least one source as the source travels its path, said different combinations ranging from one sensor to multiple sensors activated by at least one source at different times during travel along the path by the source; and a converter, the converter disposed to convert current combined activation/deactivation states of sensors in the array into a digital signal representative of a current position of the member.
It will therefore be seen that a technical advantage of the APD invention is that it relies on both normal and abnormal state detection in determining absolute position. The invention further eliminates the need for mechanical structure whose sole purpose in prior art APDs has been to avoid abnormal state detection. Both of these advantages contribute to an APD that is robust and reliable. Moreover, the APD is no longer limited to a best possible detection resolution that is defined by the physical number of sensors in an array. Best possible resolution in the inventive APD is defined by the number of discrete activation/deactivation states of the array that the source can activate during travel of the marker. Using binary state sensors such as Hall Effect devices, for example, it will be seen that there are potentially up to 2n discrete activation/deactivation states of an array having n sensors.
A further technical advantage of the APD invention is that it is well suited to high speed digital service. Being non-contact in nature, the inventive APD avoids all the operational speed limitations of mechanical APDs of the prior art. Further, the inventive APD detects current absolute position using a current activation/deactivation state of the sensors as a basis. Hardware and software techniques are well suited to conversion of a stream of such current activation/deactivation states into a digital signal at high speed.
A yet further technical advantage of the APD invention is that it is scalable. A current activation/deactivation state of multiple interrelated arrays may easily be resolved into a current positional state of a moving assembly. If desired, such overall resolution may be accomplished more efficiently by concurrent hardware or software monitoring of the combined condition of all arrays, as opposed to monitoring individual arrays and then aggregating the results in a separate operation.
Another technical advantage of the APD invention is that it is bidirectional. This advantage applies whether the invention is embodied on a closed loop or open path system. In either type of system, the inventive APD operates regardless of the direction of travel, since detection of absolute position is based on a monitored current activation/deactivation state of the sensor array. Moreover, it will be appreciated that for the same reason, the inventive APD operates to detect absolute position in the presence of reciprocating motion.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.